Interleukin(IL)-27 is a heterodimeric type I cytokine in the IL-12 cytokine family with reported roles in cancer, infectious disease, and autoimmunity. However, the literature reports conflicting roles for IL-27 for either ameliorating or potentiating inflammatory conditions, especially within the gut. The majority of the literature describing the functions of IL-27 focuses on T cell biology, resulting in a paucity of knowledge on how IL-27 may act on its primary cellular source: myeloid cells such as macrophages. The objective of this study was to characterize the effect of IL-27 on murine macrophages and determine if macrophages may mediate any potential effects of IL-27 on the colon epithelium. Here we found that IL-27 activated murine macrophages in a manner similar to interferons (IFN). RNA sequencing followed by validation with real time RT-qPCR revealed that IL-27 induced the transcription of genes associated with interferon signaling and pathogen responses in macrophages. Using gene specific knockout mice, we demonstrated that this IL-27-induced gene expression was dependent on STAT1, independent of IL-27-induced IFN-γ, and selectively dependent on IL-27-induced type I interferons. IL-27 also increased macrophage secretion of TNF-α and IFN-γ, consistent with an activated phenotype. IL-27 increased surface expression of MHC II as determined by flow cytometry in a STAT1-dependent, IFN-independent manner. To determine the functional impact of the observed IL-27-induced gene and protein upregulation, we investigated the ability of IL-27 to promote viral or bacterial clearance in macrophages. IL-27 reduced vaccinia virus infection of macrophages and, in a separate experiment, also reduced the release of mouse cytomegalovirus by infected macrophages to subsequently decrease secondary viral infection of a susceptible cell line. In contrast, IL-27 was ineffective in reducing macrophage infection by Salmonella, likely due to a lack of nitric oxide production. Co-cultures of macrophages and colon epithelial organoids were used to evaluate the ability of macrophages to mediate the effects of IL-27 on murine colon epithelial cells, which do not respond directly to IL-27. RNA sequencing of colonoids co-cultured with IL-27-stimulated macrophages detected increased expression of gene pathways crucial for pathogen responses in colon epithelial organoids. In conclusion, our data provide novel mechanistic and functional insights into the shared and divergent effects of IL-27 and interferons on both non-activated resident and classically activated macrophages.
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